8HI(g) + H2SO4 → 4I2(g) + H2S(g) + 4H22O(l) Iodine is a strong reducing agent , so it oxidises itself losing electrons to form Iodine and it reduces sulpher which form hydrogen sulhpide and the rest rect to form water.
NaI + H2SO4 --> HI + NaHSO4 then the HI goes onto reduce the SO42- 2HI + H2S04 --> SO2 + I2 + 2H2O then HI reduces the SO2 6HI + SO2 --> H2S + 3I2 + 2H2O
It is a progressive reduction NaBr does only the first two (with Br instead of I) NaCl does only the first one (with Cl instead of I)